Shaped charges, lead-free liners, and methods for making lead-free liners

ABSTRACT

A liner for a shaped charge may consist essentially of dendritic copper powder compressed under sufficient pressure to cause the dendritic copper powder to behave as a nearly solid mass. A shaped charge may include a housing and a quantity of explosive provided in the housing. A liner is positioned in the housing so that the explosive is located between the liner and the housing. The liner is compressively formed from a mixture of dendritic copper powder and a lubricant, the mixture comprising from about 90 percent by weight to less than 100 percent by weight dendritic copper powder and from more than 0 percent by weight to about 10 percent by weight lubricant.

TECHNICAL FIELD

This invention relates to shaped explosive charges in general and more specifically to liners for shaped explosive charges.

BACKGROUND

Shaped explosive charges are known in the art and may be used, for example, to form hydraulic openings or perforations in wellbores. The wellbore must be perforated because the casing of a wellbore is commonly retained within the wellbore by filling the annulus between the casing and wellbore with cement. In addition to retaining the casing within the wellbore, the cement also hydraulically isolates from one another the various formations penetrated by the wellbore.

A typical shaped charge for wellbore perforation comprises a bell-shaped housing having an open end for receiving a quantity of high-explosive, such as RDX, HMX, or HNS. A liner, typically of conical shape, is positioned within the open end of the housing so that the high-explosive is contained between the liner and the housing. The shaped charge may then be placed in a suitable perforation “gun” and lowered into the wellbore to perforate the same. When detonated, the high explosive collapses the liner and ejects it from the open end of the housing at an extreme velocity (i.e., hypersonic) in a pattern commonly referred to as a “jet.” The jet penetrates the wellbore casing, the cement, as well as portions of the surrounding formation. It is generally believed that, at such extreme velocities, the penetration process is hydrodynamic, with the jet and the “target” behaving as incompressible fluids. Consequently, the inherent mechanical strengths of the jet and target material are of little importance.

Generally speaking, it is desirable to perforate the formation surrounding the wellbore to a significant degree, referred to as penetration depth, in order to provide efficient hydraulic communication between the formation and the wellbore. The penetration depth may be increased by increasing the quantity of explosive provided within the housing, which may be appropriate in some cases. In addition, the penetration depth can also be affected by the shape and/or composition of the liner, as is known in the art.

The liners for shaped charges are usually formed from copper, although other materials have been tried and may be used as well. However, copper has been found to be generally preferable in most applications due to its high performance and low cost. While the copper may be formed into the particular shape (e.g., typically conical) from an ingot of solid metal, it is more common to form the liner from copper powder by pressing the copper powder in a form or mold. In order to ensure that the compressed copper powder remains in the desired compacted form, it has proven necessary to mix the copper powder with a binder material. As its name implies, the binder material binds together the copper powder and also provides the liner with sufficient green strength to allow it to be incorporated into the shaped charge and withstand subsequent handling without disintegrating.

The binder material typically comprises lead powder and is added in significant quantities, generally comprising about 20 weight percent or so of the liner. While being effective as a binder, the presence of lead is disadvantageous from manufacturing and environmental standpoints. For example, personnel must be protected from the lead during fabrication and subsequent handling of the liners. In addition, the detonation of the shaped charge in the wellbore will cause the lead from the liner to be introduced into the formation and wellbore environment.

Partly in an effort to avoid the problems with powdered lead binders, other powdered metals, such as bismuth, silver, gold, tin, uranium, antimony, zinc, cobalt, and nickel have been tried with varying degrees of success. Unfortunately, however, none of these other binder materials has proven entirely satisfactory in practice for a number of reasons, and lead powder binders continue to be widely used.

SUMMARY OF THE INVENTION

A liner for a shaped charge according to one embodiment may consist essentially of dendritic copper powder compressed under sufficient pressure to cause the dendritic copper powder to behave as a nearly solid mass. Another embodiment may consist essentially of a mixture of dendritic copper powder and a lubricant compressed under sufficient pressure to cause the mixture to behave as a nearly solid mass. Another embodiment of a liner for a shaped charge may comprise at least 70% by weight dendritic copper powder.

A shaped charge according to one embodiment of the present invention may include a housing and a quantity of explosive provided in the housing. A liner is positioned in the housing so that the explosive is located between the liner and the housing. The liner is compressively formed from a mixture of dendritic copper powder and a lubricant, the mixture comprising from about 90 percent by weight to less than 100 percent by weight dendritic copper powder and from more than 0 percent by weight to about 10 percent by weight lubricant.

A method for producing a liner for a shaped-charge explosive may involve providing a mixture consisting essentially of dendritic copper powder and a lubricant; and compressing the mixture under sufficient pressure to cause the mixture to behave as a nearly solid mass.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative and presently preferred exemplary embodiments of the invention are shown in the drawings in which:

FIG. 1 is a cross-sectional view in elevation of a shaped charge having a lead-free liner according to one embodiment of the invention;

FIG. 2 is a scanning electron micrograph of dendritic copper powder that may be used to construct lead-free shaped charge liners; and

FIG. 3 is a schematic process diagram of a method for forming a lead-free shaped charge liner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A shaped charge 10 having a lead-free liner 12 is illustrated in FIG. 1 and may comprise a bell-shaped housing 14 sized to receive a quantity of explosive material 16 as well as the lead-free liner 12. Although not shown in FIG. 1, shaped charge 10 may also be provided with an initiator and/or a detonating cord in order to detonate the explosive material 16.

In the embodiment shown and described herein, the shaped charge 10 is configured to be used in “down-hole” applications to perforate wellbores and surrounding formations. As such, the shaped charge 10 is sized to be received by a perforation gun (not shown), that may be lowered into the wellbore. Generally speaking, such perforation guns are configured to receive a plurality of shaped charges, thereby allowing many separate perforations to be formed in the wellbore. When initiated, the explosive material 16 collapses the lead-free liner 12 which forms a jet (not shown). The jet travels generally along the longitudinal axis 18 of shaped charge 10, perforating the wellbore casing, the cement surrounding the casing, as well as portions of the formation.

In accordance with the teachings provided herein, the lead-free liner 12 may be formed substantially entirely of dendritic copper powder 20 (FIGS. 2 and 3). That is, the liner 12 does not require the presence of a binder, lead or otherwise. Generally speaking, the dendritic copper powder 20 should comprise at least about 70 percent by weight of the lead-free liner 12, such as at least about 90 percent by weight of the lead-free liner 12, and more preferably about 100 percent by weight (not including the presence of a lubricant, as described below). Put in other words, it will be generally advantageous to form the liner 12 substantially entirely from dendritic copper powder 20 (with the exception of a lubricant), with only minimal amounts of non-dendritic copper powders and/or other materials which may be present, and which may be generally regarded as impurities that do not materially affect the basic characteristics of the dendritic copper powder composition and liners made therefrom.

The dendritic copper powder 20 may comprise any of a wide range of particle sizes and mixtures of particle sizes so long as the particle sizes allow the dendritic copper powder 20 to be compressed and achieve the green strengths and densities described herein. Generally speaking, acceptable results can be obtained with powder sizes in the following ranges: TABLE 1 Mesh Size Weight Percent 150  7%-11% 200 16%-24% +325 30%-40% −325 37%-44%

Alternatively, good results have been obtained with dendritic copper powder mixtures comprising about 95 percent by weight particles smaller than 325 mesh.

The dendritic copper powder 20 may be prepared by any of a wide range of electrolytic deposition processes known in the art and is currently commercially available from a wide range of suppliers. By way of example, in one embodiment, a suitable supply of dendritic copper powder 20 is available from Phelps Dodge Corporation of Phoenix, Ariz. (US). Generally speaking, the dendritic copper power 20 should be substantially free of impurities, with impurity levels of less than about 1 weight percent providing acceptable results.

A small quantity of a lubricant 22 (FIG. 3) may be mixed with the dendritic copper powder 20 to form a mixture 24. The addition of the lubricant 22 will assist in the subsequent compression of the mixture 24 in a suitable mold or form (not shown) in order to cause the mixture 24 to behave as a nearly solid mass, thus forming the liner 12. The lubricant 22 may be present in a range of about 10 percent by weight to less than about 0 percent by weight, and more preferably in a range of about 1 percent by weight to about 0.75 percent by weight. Lubricant 22 may comprise any of a wide range of lubricants now known in the art or that may be developed in the future that would be suitable for the particular application. Consequently, the present invention should not be regarded as limited to any particular lubricant. However, by way of example, in one embodiment, the lubricant 22 may comprise lithium stearate. Alternatively, graphite (e.g., 1651 graphite), or a combination of lithium stearate and graphite, may be used as the lubricant 22.

In addition to a lubricant 22, small amounts (e.g., generally less than about 5 percent by weight) of a higher density metal powder may be added to increase the green density of the desired product (e.g., charge liner 12). For example, powdered molybdenum, tungsten, and mixtures thereof, may be added in quantities of up to about 5 weight percent in order to increase the green density of the charge liner 12.

Referring now primarily to FIG. 3, once a mixture 24 has been prepared, e.g., from a supply of dendritic copper powder 20 and a supply of a lubricant 22, it may be formed into the desired product (e.g., liner 12) by any of a wide range of forming processes 26 now known in the art or that may be developed in the future that are (or would be) suitable for forming the powder mixture 24 so that it behaves as a nearly solid mass. An exemplary forming process 26 that may be utilized is a cold compaction process, although other forming processes, such as hot and cold isostatic pressing processes, may also be used.

If the mixture 24 is to be used to form a liner 12 for an explosive shaped charge of the type suitable for wellbore perforation, it will be generally desirable to compress the mixture 24 to a degree sufficient to provide the liner 12 with the desired green strength. For example, when compressed under a pressure of about 30 tons/in² (tsi) (about 4.14×10⁸ Pa) copper powder mixtures 24 prepared in accordance with the teachings provided herein will acquire green strengths in a range of about 3800 pounds per square inch (psi) (about 2.62×10⁷ Pa) to about 5000 psi (about 3.45×10⁷ Pa) and green densities in a range of about 7 to about 8 g/cc. Generally speaking, experiments have confirmed that mixtures prepared in accordance with the teachings provided herein generally provide higher green strengths and comparable green densities under the same compressive pressures as compared to those achieved by a conventional copper powder/lead binder mixture.

COMPARATIVE EXAMPLES

Two different mixtures “A” and “B” comprising dendritic copper powder 20 were compared with results obtained from a conventional (i.e., non-dendritic) copper powder mixture (“Conventional”). More specifically, Mixture “A” comprised dendritic copper powder (about 95%-325 mesh), and about 0.75 percent by weight lithium stearate. Mixture “B” comprised mixture “A” with about 1 percent by weight graphite added (i.e., about 0.75 percent by weight lithium stearate and about 1 percent by weight graphite). The conventional copper powder mixture, commonly referred to as “CLG-80” comprised 80 percent by weight non-dendritic copper powder (56%-150/+325 mesh, 25%-325 mesh), 19 percent by weight lead powder, and 1 percent by weight carbon graphite as a lubricant.

A first comparative test was used to measure the comparative green densities and green strengths of compacted rods or bars made from the conventional mixture and Mixture “A.” More specifically, the first test comprised a die wall friction test and was conducted in accordance with the procedures specified by ASTM B-328. Briefly, ASTM B-328 involves the compression of powder contained within a cylindrical opening formed within a die. The cylindrical opening has a diameter of 0.125 inches (in) (about 7.125 mm) and a length of 1.0 in (about 2.54 mm). The powders were compacted from the top only at a pressure of about 30 tons/in² (tsi) (about 4.14×10⁸ Pa). The resulting compacted rods or bars of the samples were then cut into four equal segments (A, B, C, and D), the green densities and strengths of which were then measured in accordance with ASTM testing methods.

The results of the test are presented below in Table 2. TABLE 2 Conventional (Cu80Pb18C1) Mixture “A” Green Green Green Density Strength Green Density Strength Location (g/cc) (psi) (g/cc) (psi) Top (A) 7.34 2050 7.17 4150 B 7.29 1900 6.71 2750 C 6.87 1150 6.27 1800 Bottom (D) 6.27 550 5.99 1400

As indicated in Table 2, at 30 tsi compaction pressure, the green strength of a bar formed from Mixture “A” exceeded that of a bar formed from conventional powder at any position along the length of the respective sample bars. The green density of a bar formed from Mixture “A” was generally comparable, although slightly lower, than that associated with a bar formed from the conventional powder. Lubricity measured by the die wall friction test shows large gains in green strengths with comparable green densities for Mixture “A” compared to the conventional mixture.

Average green strengths and densities for the conventional powder, Mixture “A,” and Mixture “B” were also obtained by compressing the powders at various pressures, i.e., 5, 10, 30, and 48 tsi (about 6.9×10⁷, 1.38×10⁸, 4.14×10⁸, and 6.62×10⁸ Pa) to produce 3 separate compressed samples at each compaction pressure. The average values for each of the three samples at each of the pressures are presented in Table 3: TABLE 3 Conventional (Cu80Pb19C1) Mixture “A” Mixture “B” Green Green Green Green Green Green Pressure Density Strength Density Strength Density Strength (tsi) (g/cc) (psi) (g/cc) (psi) (g/cc) (psi)  5 5.80 311 5.32 620 5.30 640  5 5.79 290 5.34 648 5.32 630  5 5.81 339 5.33 651 5.31 600 Avg. 5.80 313 5.33 640 5.31 620 10 6.62 1013 6.16 1570 6.09 1510 10 6.63 1002 6.16 1540 6.08 1450 10 6.58 936 6.18 1610 6.09 1600 Avg. 6.61 984 6.17 1570 6.09 1520 30 8.04 3697 7.45 4940 7.28 4440 30 8.07 3784 7.45 5190 7.27 4640 30 8.06 3883 7.40 4920 7.29 4530 Avg. 8.06 3788 7.43 5020 7.28 4537 48 8.53 5342 7.81 6870 7.58 6200 48 8.53 5326 7.80 6820 7.59 6150 48 8.50 5357 7.84 6530 7.61 5950 Avg. 8.52 5341 7.82 6740 7.59 6100

As evidenced by the data in Table 3, samples formed from both Mixtures “A” and “B” produced significantly higher green strengths at all compaction pressures compared to samples formed from the conventional powder. Green densities were generally comparable, although somewhat lower, compared to samples formed from the conventional powder.

Two additional mixtures, Mixture “C” and Mixture “D” were also prepared using dendritic copper powder having particle sizes shown in Table 4: TABLE 4 Mesh Size Weight Percent −100/+170  8% −170/+230 18% −230/+325 33% −325 41%

Mixture “C” also comprised about 0.75 percent by weight lithium stearate. Mixture “D” comprised Mixture “C” with about 1 percent by weight graphite added (i.e., about 0.75 percent by weight lithium stearate and about 1 percent by weight graphite). Three separate samples of Mixtures “C” and “D” were compressed under a pressure of about 30 tsi (about 4.14×10⁸ Pa). The average values for each of three samples at the 30 tsi compaction pressure are presented in Table 5: TABLE 5 Conventional Mixture Mixture Mixture Mixture (Cu80Pb19C1) A B C D Green Density 8.06 7.43 7.28 7.58 7.47 (g/cc) Green Strength 3788 5020 4530 3908 3816 (psi)

As evidenced by the data in Table 5, samples formed from Mixtures “C” and “D” resulted in somewhat higher green densities, but somewhat lower green strengths when compared with Mixtures “A” and “B.” The green densities of Mixtures “C” and “D” were comparable to those achieved by the conventional powder, with the green strengths being somewhat higher.

Having herein set forth preferred embodiments of the present invention, it is anticipated that suitable modifications can be made thereto which will nonetheless remain within the scope of the invention. The invention shall therefore only be construed in accordance with the following claims: 

1. A liner for a shaped charge consisting essentially of a mixture of dendritic copper powder and a lubricant compressed under sufficient pressure to cause said mixture to behave as a nearly solid mass.
 2. The liner of claim 1, wherein said lubricant comprises one or more selected from the group consisting essentially of graphite and lithium stearate.
 3. The liner of claim 1, wherein said mixture comprises from about 90 percent by weight to less than 100 percent by weight dendritic copper powder and from more than 0 percent by weight to about 10 percent by weight lubricant.
 4. The liner of claim 1, wherein said mixture comprises about 98 percent by weight dendritic copper and about 2 percent by weight lubricant.
 5. The liner of claim 1, further comprising less than about 5 weight percent metal powder additive, said metal powder additive comprising one or more selected from the group consisting essentially of molybdenum and tungsten.
 6. The liner of claim 1, wherein said dendritic copper powder comprises electrolytically-deposited copper powder.
 7. A method for producing a liner for a shaped-charge explosive, comprising: providing a mixture consisting essentially of dendritic copper powder and a lubricant; and compressing said mixture under sufficient pressure to cause said mixture to behave as a nearly solid mass.
 8. The method of claim 7, wherein said compressing comprises a cold compaction process.
 9. The method of claim 7, wherein said compressing comprises hot isostatic pressing.
 10. The method of claim 7, wherein said compressing comprises cold isostatic pressing.
 11. The method of claim 7, wherein said compressing comprises applying to the mixture a pressure of about 30 tsi.
 12. The method of claim 11, wherein said compressing imparts to said liner a green strength in a range of about 3800 psi to about 5000 psi.
 13. The method of claim 11, wherein said compressing imparts to said liner a green density in a range of about 7 g/cc to about 8 g/cc.
 14. The method of claim 7, wherein providing a mixture further comprises: providing a supply of dendritic copper powder; providing a supply of lubricant; mixing together a portion of said supply of dendritic copper power and a portion of said supply of lubricant to produce said mixture.
 15. The method of claim 14, wherein mixing together further comprises mixing from about 90 percent by weight to less than 100 percent by weight said dendritic copper powder and from more than 0 percent by weight to about 10 percent by weight said lubricant.
 16. The method of claim 14, wherein mixing together further comprises mixing about 98 percent by weight said dendritic copper powder and about 2 percent by weight said lubricant.
 17. The method of claim 14, wherein mixing together further comprises mixing about 99 percent by weight said dendritic copper powder and about 1 percent by weight said lubricant.
 18. The method of claim 14, wherein providing a supply of dendritic copper powder comprises providing a supply of electrolytically deposited copper powder, and wherein providing a supply of lubricant comprises providing a supply of lubricant comprising one or more selected from the group consisting of lithium stearate and graphite.
 19. A liner for a shaped charge comprising at least 70% by weight dendritic copper powder.
 20. The liner of claim 19, further comprising a lubricant.
 21. The liner of claim 20, wherein said lubricant comprises one or more selected from the group consisting of graphite and lithium stearate.
 22. The liner of claim 20, wherein said lubricant comprises from more than 0 percent by weight to about 10 percent by weight.
 23. A shaped charge comprising: a housing; a quantity of explosive provided in said housing; and a liner provided in said housing so that said explosive is located between said liner and said housing, said liner being compressively formed from a mixture of dendritic copper powder and a lubricant, said mixture comprising from about 90 percent by weight to less than 100 percent by weight said dendritic copper powder and from more than 0 percent by weight to about 10 percent by weight said lubricant.
 24. The shaped charge of claim 23, wherein said mixture comprises about 99 percent by weight said dendritic copper powder and about 1 percent by weight said lubricant.
 25. The shaped charge of claim 23, wherein said explosive comprises one or more selected from the group consisting of RDX, HMX, and HNS.
 26. A liner for a shaped charge consisting essentially of dendritic copper powder compressed under sufficient pressure to cause said dendritic copper powder to behave as a nearly solid mass.
 27. The liner of claim 26, further comprising a lubricant mixed with said dendritic copper powder.
 28. The liner of claim 27, wherein said lubricant comprises one or more selected from the group consisting essentially of lithium stearate and graphite.
 29. A powder mixture consisting essentially of dendritic copper powder and a lubricant, said lubricant having a percent by weight which lies in a range from more than 0 percent to less than 10 percent, a remaining percent by weight of said mixture being said dendritic copper powder.
 30. The powder mixture of claim 29, wherein said lubricant comprises one or more selected from the group consisting of lithium stearate and graphite.
 31. The powder mixture of claim 29 further comprising a green strength in a range of about 3800 psi to about 5000 psi when said powder mixture is compressed under a pressure of about 30 tsi.
 32. The powder mixture of claim 29 further comprising a green density in a range of about 7 g/cc to about 8 g/cc when said powder mixture is compressed under a pressure of about 30 tsi. 